Proportion of nonindigenous fishes in SD by type of introduction:
Proportion of nonindigenous fishes in SD by mode of introduction:
Ecologically important invertebrate species not found in South Dakota Zebra mussels The zebra mussel Dreissena polymorpha is a small (up to 40 mm) bivalved mollusk native to rivers near the Caspian and Ural seas. It was first reported from the Great Lakes in 1988 and has since spread to the Mississipi River drainage where it will likely lead to substantial changes in unionid demographics. It was recently found near Sioux City, Iowa on the Missouri River. Its life cycle includes a free-floating larval stage (veliger) followed by juvenile and adult stages where the mussel is attached by byssal threads to firm substrata. These life-history traits contribute to the successful spread of zebra mussels in North America. The free swimming veliger attaches itself to any solid object by means of a glue and byssal threads and zebra mussels have been found on trailered boats in Virginia and California.
Rusty crayfish Non-native crayfishes are one of the most destructive invaders of aquatic ecosystems in North America. Non-native crayfishes can affect fish populations by preying on fish eggs and reducing aquatic vegetation that is important for juvenile fishes. The rusty crayfish Orconectes rusticus , native to the Ohio River drainage, is one of the most destructive crayfishes and has spread rapidly throughout the midwest. In addition to affecting fishes, the rusty crayfish can also displace native crayfishes such as O. virilis and O. propinquus. Because they need refuge from predation, rock or boulder substrates are usually an excellent predictor of where the rusty crayfish can be found. Because crayfishes are often used as fishing bait, they are easily spread from one location to another. Several states (e.g., Wisconsin) have banned the use of live crayfish as bait. These regulations have had little, if any, effect on the recreational fishing industry and serve as a way to prevent the spread of nonindigenous crayfishes. The rusty crayfish is now found in close proximity to South Dakota (Minnesota, Iowa, and Wisconsin) and may pose a threat to South Dakota waters.
Bythotrephes The spiny water flea, Bythotrephes (bith-o-TREH-feez) cederstroemi, a small planktivorous crustacean, has an average length slightly larger than 1 centimeter (0.4 inches) of which 70% is a long, sharp, barbed tail spine. First introduced into the Great Lakes ecosystem in 1984 via ballast water that was discharged into Lake Huron, they had spread to all of the Great Lakes by 1987; currently they are found in inland lakes in Michigan and Southern Ontario. Their rapid reproduction, general lack of predators, and direct competition with young fish for food enhances their ability to alter aquatic food webs. Bythotrephes eat small herbivorous crustaceans, including native Daphnids. Daphnia, however, are also an important food item for small, juvenile fish. As a result, Bythotrephes can compete directly with young fish for food. Because of their unique reproductive pattern, Bythotrephes can reproduce many times faster than fishes. Their rapid population growth enables Bythotrephes to monopolize the food supply at times, to the eventual detriment of the fish. The success of Bythotrephes in colonizing all of the Great Lakes raises the possibility that it may soon invade smaller, inland lakes in the Great Lakes basin.
Daphnia lumholtzi4 Daphnia lumholtzi is a species that has recently invaded North America. Easily identified, Daphnia lumholtzi produces much larger and more numerous spines than do North American Daphnia (see figure below). The head and tail spines may be as long as the body, which is partially covered with smaller spines. Large individuals can reach total lengths of 5.6 mm (nearly 0.25 in), making them visible to the naked eye. Scientists are concerned that Daphnia lumholtzi may have negative effects on North American ecosystems. The large spines make it difficult for young fishes (larval and juvenile stages) to consume. In the Midwest, populations of Daphnia lumholtzi tend to peak during mid-summer when juveniles of these fishes may still be dependent on zooplankton as a primary food source. Daphnia lumholtzi may spread in a number of ways. Although it likely does not swim against river currents, Daphnia lumholtzi may travel upriver in baitbuckets as well as bilge-water and livewells of recreational and commercial watercraft. It may also spread in its dormant egg stage.
New Predator Invades the Great Lakes One of the most recent additions to the Great Lakes is another tiny stowaway from Eurasia. Cercopagis pengoi is a small (< 2 mm body length) predatory crustacean that was first discovered in Lake Ontario in 1998. Cercopagis, which has become known as the "fishhook flea," possesses a tail spine that can be up to five times as long as its body. In Cercopagis, the tail spine includes a predominate curve, which separates it from the closely related Bythotrephes cederstroemi that invaded the Great Lakes in the 1980s. Because of this long, spiny, appendage, Cercopagis and Bythotrephes are often found fouling fishing lines in the Great Lakes. The clogging of reels and fouling of nets makes these exotic species potential nuisances in these systems. Both Cercopagis and Bythotrephes possess life history traits that make them good invaders. Like many other species of zooplankton, they reproduce by means of cyclic parthenogenesis, which means there is an alternation of reproductive mode. For most of the year, only females are present in the water. These females produce eggs asexually, which in a few days are released as newborn daughters. With this mode of reproduction, a single introduced individual could potentially colonize an entire lake!
It is not known what effect this new species will have on the Great Lakes ecosystem. When Bythotrephes invaded Lake Michigan, its entrance to the lake coincided with marked changes in the food web. Both Bythotrephes and Cercopagis are predators, eating other species of zooplankton that are also the primary food for many species of fish. Cercopagis is considerably smaller than Bythotrephes, so it may fall victim to predation by the larger predatory species. In addition, Cercopagis and Bythotrephes may provide additional food for fish. Bythotrephes is commonly eaten by yellow perch and alewife, although the benefit of eating this spiny species for fish is unclear due to problems they experience digesting and passing the spiny leftovers. Cercopagis also was found in alewifeguts last fall, but the potential impact of these and other fish on Cercopagis is not clear. Future research will help us understand the role of this new species in North American Lakes. ?
Spread of Exotic Cladocerans Live animals require water to be transported from lake to lake. Therefore, the control measures used for other exotic aquatic species (emptying of bait buckets and live wells, washing and drying of all gear) will also help to reduce the spread of Cercopagis. The diapausing eggs are a different story. These eggs can hatch after they have dried up or frozen, even if it is several years later. Moreover, since females carrying these eggs can "stick" to fishing gear and other recreational equipment, care must be taking to thoroughly clean all equipment after leaving a lake (instead of just allowing things to dry).
Steps for Preventing Spread of Cladocerans and Zebra Mussels by Recreational Water Users BEFORE leaving boat launch: 1) Inspect boat, trailer, and equipment 2) Remove any observed plants and animals. 3) Drain, on land, all water from the motor, livewell, bilge, and transom well. 4) Empty water from bait buckets on land, and dispose of unwanted bait in trash. AFTER leaving boat launch: Wash all equipment with 104°F water or a high pressure sprayer, OR: Dry equipment for at least five days.